Optical characterization in the vacuum ultraviolet with Variable Angle Spectroscopic Ellipsometry: 157 nm and below

As device feature sizes shrink below 0.18 μm, shorter wavelength exposure tools are being investigated to meet the requirements for higher resolution. Understanding the optical properties of thin films and substrate materials at short wavelengths (193 nm, 157 nm, and shorter) will be necessary to develop the lithographic process. Variable Angle Spectroscopic Ellipsometry (VASE) offers nondestructive and precise measurement of thin film thickness and refractive index in the wavelength range from 146 nm to 1700 nm. VASE measurements provide a complete description of the thin film optical properties, which can be used to track process changes or variations in sample structure. Recent hardware innovations have extended VASE into the vacuum ultraviolet to meet lithography requirements at 157 nm.